Paul Scherrer Institute, 5232 Villigen, Switzerland.
Rev Sci Instrum. 2023 Mar 1;94(3):034103. doi: 10.1063/5.0136665.
We introduce an effective and flexible high vacuum interface to probe the liquid phase with photoelectron photoion coincidence (liq-PEPICO) spectroscopy at the vacuum ultraviolet (VUV) beamline of the Swiss Light Source. The interface comprises a high-temperature sheath gas-driven vaporizer, which initially produces aerosols. The particles evaporate and form a molecular beam, which is skimmed and ionized by VUV radiation. The molecular beam is characterized using ion velocity map imaging, and the vaporization parameters of the liq-PEPICO source have been optimized to improve the detection sensitivity. Time-of-flight mass spectra and photoion mass-selected threshold photoelectron spectra (ms-TPES) were recorded for an ethanolic solution of 4-propylguaiacol, vanillin, and 4-hydroxybenzaldehyde (1 g/l of each). The ground state ms-TPES band of vanillin reproduces the reference, room-temperature spectrum well. The ms-TPES for 4-propylguaiacol and 4-hydroxybenzaldehyde are reported for the first time. Vertical ionization energies obtained by equation-of-motion calculations reproduce the photoelectron spectral features. We also investigated the aldol condensation dynamics of benzaldehyde with acetone using liq-PEPICO. Our direct sampling approach, thus, enables probing reactions at ambient pressure during classical synthesis procedures and microfluidic chip devices.
我们介绍了一种有效的、灵活的高真空接口，用于在瑞士光源真空紫外（VUV）光束线上用光电离符合（liq-PEPICO）光谱探测液相。该接口包括一个高温护套气体驱动的蒸发器，它最初产生气溶胶。颗粒蒸发并形成分子束，分子束被 VUV 辐射掠入射和电离。利用离子速度图成像对分子束进行了表征，并优化了 liq-PEPICO 源的蒸发参数以提高检测灵敏度。记录了 4-丙基愈创木酚、香草醛和 4-羟基苯甲醛（每种 1g/l）的乙醇溶液的飞行时间质谱和光电离质量选择阈值光电光谱（ms-TPES）。香草醛的基态 ms-TPES 带很好地重现了参考室温光谱。4-丙基愈创木酚和 4-羟基苯甲醛的 ms-TPES 是首次报道。用运动方程计算得到的垂直电离能再现了光电子光谱特征。我们还使用 liq-PEPICO 研究了苯甲醛与丙酮的羟醛缩合动力学。因此，我们的直接采样方法可以在常压下探测经典合成过程和微流控芯片设备中的反应。
